1. Technical Field
The present invention relates to the art of air-ride axle/suspension systems for heavy-duty vehicles, such as tractor-trailers or semi-trailers, which cushion the ride and stabilize the vehicle during operation. More specifically, the invention relates to pneumatic control of the air springs of an air-ride axle/suspension system, and in particular to a height control valve which regulates the flow of air out of the air springs.
2. Background Art
Heavy-duty vehicles, such as tractor-trailers or semi-trailers, typically include one or more leading or trailing arm suspension assemblies that connect the wheel-bearing axles of the vehicle to the frame of the vehicle. Early suspension designs included heavy spring suspensions which resulted in a relatively rough ride to the caigo and did not allow loads to equalize among the axles in all situations, thus creating the need for a suspension system with soft ride characteristics and efficient equalization characteristics. The subsequent development of air suspension systems provided load equalization among multiple axles for semi-trailers as well as improved tide quality for individual axles.
As a result, heavy-duty vehicles that transport freight often include leading or trailing arm air-ride axle/suspension systems, which use air springs to cushion the ride of the vehicle Pneumatic control of these air springs is an important feature of air-ride axle/suspension systems.
More particularly, it is important for a cushioned vehicle ride, and for optimum axle/suspension system performance and longevity, to attempt to maintain a consistent, predetermined distance between the vehicle frame and the travel surface This predetermined distance is known in the art as the design ride height of the vehicle. To establish the design ride height of a vehicle, the operating conditions of the vehicle must be considered. That is, when a heavy-duty vehicle executes certain maneuvers, such as making a hard turn or traveling over rough terrain, the forces imposed on the axle/suspension system by such maneuvers cause the axle/suspension system to articulate, or pivot and/or flex beneath the vehicle frame which the system supports. Typically, an axle/suspension system is designed so that the anticipated range of articulation occurs about a nominal predetermined position, and that nominal position is set as the design ride height of the vehicle.
After a heavy-duty vehicle is loaded with freight, or freight is unloaded from the vehicle, the air springs of the axle/suspension system are adjusted to ensure that the vehicle is at design ride height before traveling. That is, when the vehicle is loaded with freight and the air springs of the axle/suspension system are compressed causing the vehicle frame to be positioned below design ride height or closer to the travel surface, compressed air is supplied to the air springs, thereby inflating/extending them and in turn causing the axle/suspension system to raise the vehicle frame to the design ride height Conversely, when the vehicle is unloaded and the air springs of the axle/suspension system are extended causing the vehicle frame to be positioned above design tide height or further away from the travel surface, air is exhausted from the air springs, thereby deflating/compressing them until the axle/suspension system lowers the vehicle frame to the design ride height. To control the flow of air into the air springs, and the exhaustion of air from the air springs, a mechanically operated valve typically is employed, and is known in the art as a height control valve or leveling valve. Adjustments to the height control valve and the linkage that controls activation of the valve enable the design ride height to be achieved before the vehicle travels over the road.
As the vehicle travels over the road and the driver executes maneuvers that cause the axle/suspension system to articulate between a position that compresses the air springs and a position that extends them, the height control valve acts to maintain the design ride height That is, when the air springs are compressed, the height control valve supplies air to the springs from a vehicle air reservoir. Conversely, when the air springs are in an extended position, the height control valve exhausts air from the springs to atmosphere The amount of air that is supplied or exhausted is based on the duration of the articulation and the flow late of the height control valve at a given position. However, height control valves of the prior art sometimes allow over-exhaustion of air from the air springs when the vehicle is loaded.
More particularly, when a vehicle is carrying significant cargo, an increased load is placed on the air springs of the axle/suspension system. In response to such an increased load, the height control valve introduces compressed air from the vehicle air reservoir into the air springs, thereby increasing the air pressure within the air springs in older to regain and maintain design ride height. Then, when exhaustion of air from the air springs is necessary to maintain design ride height, the increased pressure in the air springs raises the rate of flow of air exiting the air springs through the height control valve. Such a potentially increased rate of exhaust may enable too much compressed air to exit the air springs, thereby reducing the ability of the compressed air reservoir to rapidly re-inflate the air springs when required. For example, typical air spring pressures on a loaded vehicle may be between about 90 pounds per square inch (psi) and about 100 psi, which means that, for a loaded vehicle, the typical pressure differential between the air springs and atmosphere is from about 90 psi to about 100 psi Vehicle air reservoir pressures typically are between about 100 psi to about 130 psi. Therefore, the typical pressure differential between the vehicle air reservoir and the air springs may range from about 0 psi to about 40 psi. Since height control valves of the prior art exhaust air at a rapid rate, when the air springs are under an increased load from a freight-laden vehicle, this pressure differential may be too small to enable the vehicle air reservoir to provide sufficient compressed air to the air springs for regaining and maintaining design ride height in certain instances.
Thus, for a loaded vehicle, when the axle/suspension system articulates so that one or more of the air springs is in an extended position and the height control valve of the prior art exhausts air from the springs, the air may exhaust so rapidly that the reservoir may not be able to supply enough compressed air to rapidly refill the air springs when the event causing the extension has passed. More specifically, such a rapid refill may be necessary if the axle/suspension system articulates quickly to an air spring compressed position after it has articulated to the air spring extended position, which may be encountered in vehicle maneuvers such as turning or driving over rough terrain. As a result, when the axle/suspension system then articulates to the air spring compressed position, the actual ride height may be undesirably below the design ride height. This is referred to as dynamic ride height drift. In a maneuver such as a hard turn, the dynamic ride height drift may be considerable.
Therefore, if the amount of air that the height control valve permits to be exhausted is too great, the axle/suspension system might not be able to maintain the design ride height, which potentially can lead to damage of the axle/suspension system. More particularly, the air springs of the axle/suspension system can become damaged when the pressure within the air springs is too low to maintain design ride height This potential damage can occur when the internal bumper within the air spring contacts the air spring bead plate with a violent blow or series of blows. In addition, other vehicle damage such as crushed frame cross members and/or bent suspension beams can also occur. This disadvantage of prior art height control valves makes it desirable to develop a height control valve that is capable of regulating the exhaust rate on a loaded vehicle
The present invention solves the above-described problem involving rapid exhaustion of air from the air spring of an axle/suspension system through the height control valve of a loaded vehicle by utilizing a height control valve that regulates the exhaust late of air from the air spring If desired, the concepts of the present invention may also be applied to a related problem where the height control valve of an unloaded or lightly loaded vehicle over-inflates the air spring with air supplied from the air reservoir. By providing a height control valve that is capable of regulating the rate of air flow from the air reservoir into the air spring, over-inflation of the air spring can be minimized or prevented.